Let’s say, A has just found out that someone took his wallet while he was away. He is talking with his friend B about it:
1). It’s XXX, I know it.
2). It was XXX, I know it.
3). It must/could/might/may be XXX.
4). It must/could/might/may have been XXX.
Which is correct?
Ha ha. I’m dead, I’m a dead man.
Okay, I have no problem with 2 and 4, they are about something happened in the past; I have come into the usage of 1, thugh I still don’t feel completely comfortable with it, but it is used to show, maybe, comfirmation; but isn’t 3 used to show your guess about something at present or in the future?
It’s used to show your guess about something amnd your guess in the present is that it is XXX who now has your wallet (or its contents or the proceeds of its contents).